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Montoya, who is a Colombian citizen, is in his final season with Earnhardt Ganassi Racing and will leave NASCAR to drive for Penske Racing in the IndyCar Series at the end of the 2013 season.

According to Forbes, the IRS contends that Montoya had $9.5 million in taxable income in 2007 and 2008, while Montoya and his wife reported their taxable income as $2.4 million for the two years.

Montoya attests he had $800,000 more in income than he reported on his tax returns but is disputing other parts of the IRS audit.

The dispute deals with a company he formed to handle earnings from the use of his image and name. He created the new company when moving from Formula One to NASCAR and the deductions he claimed in transitioning from a foreign company to a domestic company are part of the dispute, according to Forbes, as well as the tax breaks claimed for an $8.7 million Lear jet.

The government has not charged Montoya with any crime. He is challenging the IRS audit of his earnings in U.S. Tax Court.